Lactic acid is an important industrial chemical, which finds use as a feedstock in the biopolymer industry. Today, virtually all large scale production of the lactic acid available commercially is manufactured by fermentation processes, see for example Strategic Analysis of the Worldwide Market for Biorenewable Chemicals M2F2-39, Frost and Sullivan, 2009. In a typical fermentation process, biomass is fermented with microorganisms to produce either D- or L-lactic acid, most commonly L-lactic acid. Companies such as Cargill and Purac (now Corbion) operate large-scale fermentation processes for the production of optically active lactic acid. Many patent publications relate to recovery of lactic acid from fermentation mixtures, which can be challenging, and a number of patent documents rely on the preparation of a complex between lactic acid and an amine for the recovery (see, for example, U.S. Pat. Nos. 4,444,881, 5,510,526).
Chemical processes for preparing lactic acid from carbohydrates are known. For example, GB 400,413, dating from 1933, describes an improved process for preparing lactic acid or lactates comprising reacting a carbohydrate-containing material with a strong alkali at a temperature of at least 200° C., preferably at a pressure of at least 20 atmospheres, and recovering the lactic acid so produced by adding sulfuric acid or zinc sulfate to the reaction mixture. Hydrocyanation of acetaldehyde has also been used as a synthetic route for accessing lactic acid.
WO 2012/052703 describes an improved process for the production of a complex of lactic acid and either ammonia or an amine, which does not involve production of lactic acid by fermentation. The process comprises reacting one or more saccharides with barium hydroxide to produce a first reaction mixture comprising barium lactate, and contacting at least part of the first reaction mixture with ammonia or an amine and with carbon dioxide, or with the carbonate and/or bicarbonate salt of ammonia or an amine, to produce a second reaction mixture comprising the complex and barium carbonate. This process, which involves preparation of barium salts, has significant advantages over prior art processes. It does, however, have some disadvantages: specifically, if it is required to recycle the barium, a barium carbonate calcination step is required. Calcination (also referred to as calcining) is a thermal treatment process in absence of air applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction. The process of calcination derives its name from its most common application, the decomposition of calcium carbonate (limestone) to calcium oxide (lime) and carbon dioxide. The terms calcination, and calcine (the product of calcination), are typically used regardless of the actual minerals undergoing thermal treatment. Whilst barium carbonate calcination is feasible, the technology is not currently widely operated at industrial scale.
In addition, carrying out the process described in WO2012/052703 on an industrial scale requires facilities adapted to handle and transport large quantities of barium salts. Processing solutions for large scale use of barium salts exist. However, there remains a need for improved processes for generating lactic acid and related materials, which still provide acceptable yields of complex but which avoid the disadvantages associated with use of barium salts.